Ten more people have been killed by a US drone strike against suspected militants in Pakistan, with the aircraft firing its missiles into a gathering mourning one of two fighters killed in a similar atttack the previous day.

Two Pakistani intelligence officials say four missiles were fired at the village of Mana Raghzai in South Waziristan near the border with Afghanistan on Sunday morning.

At the time of the attack, suspected militants had gathered to offer condolences to the brother of a militant commander killed during another US unmanned drone attack on Saturday. The brother was one of those who died in the Sunday morning attack. The Pakistani officials said two of the dead were foreigners and the rest were Pakistani.

It brought to 12 the total number of people killed in two days and was the sixth American drone strike over the last two weeks. The US government considers the drone campaign a vital tool in the war against al-Qaida and the Taliban.

The drone campaign has been a source of deep frustration and tension between the US and Pakistan. Under Barack Obama the US has stepped up its drone campaign in the Pakistani border areas as a way to combat insurgents and terrorists who use Pakistan as a base for attacks against American and Nato forces in Afghanistan. The number of drone attacks has eased in recent years.

Many Pakistani military commanders are believed to secretly support the drone campaign. But among the Pakistani public, where the US is viewed with mistrust, the strikes are considered an affront to the country's sovereignty.

The attacks are complicating efforts for the US and Pakistan to come to an agreement over reopening the supply routes to Nato and American forces in Afghanistan. US air strikes inadvertently killed 24 Pakistani soldiers in November, prompting Islamabad to block the supply lines into Afghanistan. Pakistan wants an apology and an end to drone strikes before it reopens them.